The active site of a number of copper-containing metalloproteins which show a large variation in function has been found to contain a binuclear copper unit designated as "type 3" copper. These metalloproteins include the hemocyanins, tyrosinases, laccases, and ceruloplasmins. This binuclear copper unit exhibits unusual electronic structure properties, the origins of which have not been determined. The objectives of this proposal are to obtain the geometric and electronic structure of the active site for each of these proteins, to elucidate the origin of the unusual spectroscopic properties relative to simple copper complexes, and to determine if structural variations in active site correlate with the variations in protein function. This will be accomplished through the use of a variety of physical methods (e.g., EPR, resonance Raman, optical and dichroism techniques) and chemical perturbations. New spectroscopic methods for the study of metalloproteins and the extension of existing techniques and theory are also a part of this study. A description of the "type 3" copper will then be obtained through the interpretation of the results of these studies by the application of existing bonding theories (in particular, ligand field theory) to the unusual electronic structural properties.